System and method for securing a plate to the spinal column

ABSTRACT

The present invention is directed to a drill guide and methods of using a drill guide with a plate having at least one slotted hole extending therethrough. The drill guide positions a bone engaging fastener away from the ends of the slot, allowing compression or distraction of the bony segment to which the plate is attached.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/417,402 filed Oct. 13, 1999, pending.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of instrumentationand systems for the spine, and more particularly to instrumentation andsystems for use in engaging plates to the spine.

Bony structures are subject to defects and trauma which require a plateto be secured thereto in order to stabilize the bony segment as it healsor fuses. For example, the spine is subject to various pathologies thatcompromise its load bearing and support capabilities. Such pathologiesof the spine include, for example, degenerative diseases, the effects oftumors and, of course, fractures and dislocations attributable tophysical trauma. Spinal surgeons have addressed these problems using awide variety of instrumentation in a broad range of surgical techniques.The use of elongated rigid plates has been helpful in the stabilizationand fixation of the lower spine, most particularly in the thoracic andlumbar spine. These same plating techniques have found some level ofacceptance by surgeons specializing in the treatment of the cervicalspine.

Many spinal plating systems have been developed in the last couple ofdecades to address some of the needs and requirements for spinal andother bony segment fixation systems. However, even with the more refinedplating system designs, there still remains a need for a system thateffectively addresses the requirements for such a system. For example,there remains a need for systems and methods for inserting bone engagingfasteners which allow compression and extension of the bony segment towhich the plate is attached after the fasteners are inserted. Thepresent invention is directed to satisfying these needs, among others.

SUMMARY OF THE INVENTION

The present invention provides a drill guide for forming holes through aplate in a vertebra into which bone engaging fasteners are inserted toengage the plate to the vertebra. The drill guide positions the boneengaging fastener away from the ends of a slotted hole through plate.

The present invention also provides a bone fixation system that includesa plate and a drill guide. The plate includes at least one slotted holeextending therethrough. The drill guide is positionable on the platesuch that a hole drilled through the drill guide spaces the screw fromthe ends of the slotted hole.

The present invention further provides methods for securing a plate toupper and lower vertebrae of a spinal column segment. The plate is fixedto one of the vertebra. A bone engaging fastener engaged to the othervertebra is positioned away from the ends of a slot extending throughthe plate. The fastener can thus accommodate extension andpost-operative settling of the spinal column segment surgeon selectivelyapplies either a compression or distraction load to the spinal columnsegment with the plate secured to the spinal column segment by the boneengaging fastener.

These and other forms, embodiments, aspects, features, objects of thepresent invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of an anterior plating system accordingto the present invention.

FIG. 2 is a top perspective view of the anterior plating system of FIG.1 with the bone screws locked in place.

FIG. 3 is a top perspective view of the anterior plating system of FIG.1 with bone screws translated in a slot of the plate.

FIGS. 4( a)-4(f) are top plan views of fixation plates of the presentinvention provided in different sizes and configurations.

FIGS. 5( a)-5(f) are top plan views of washers of the present inventionprovided in sizes and configurations corresponding to the plates inFIGS. 5( a)-5(f).

FIG. 6 is a side elevational view of a bone screw according to oneaspect of the present invention.

FIG. 7 is a side elevational view of a locking fastener according toanother aspect of the present invention.

FIGS. 8( a)-8(k) are various views and sections of washers according tothe present invention.

FIG. 9 is a top plan view of a first end of the fixation plate of thepresent invention.

FIG. 10 is a cross-sectional view taken through line 10-10 of FIG. 9.

FIG. 11 is an end elevational view of the plate of FIG. 9.

FIG. 12 is a top plan view of a second end of the fixation plate of thepresent invention.

FIG. 13 is a cross-sectional view taken along line 13-13 of FIG. 12.

FIG. 14 is an enlarged cross-sectional view taken through line 14-14 ofFIG. 12.

FIG. 15 is a top plan view of an intermediate portion of the fixationplate of the present invention.

FIG. 16 is a cross-sectional view taken through line 16-16 of FIG. 15.

FIG. 17 is an enlarged cross-sectional view taken through line 17-17 ofFIG. 15.

FIG. 18 is an enlarged cross-sectional view taken through line 18-18 ofFIG. 15.

FIG. 19 a is a partial sectional view of the anterior plate assembly ofthe present invention with the screws disposed through the holes at thefirst end of the plate and engaged in a vertebra.

FIG. 19 b is a partial sectional view of the anterior plate assembly ofthe present invention with the screws disposed through the slots of theplate and engaged in a vertebra.

FIGS. 20( a)-20(f) illustrate various instruments and steps of a methodaccording to another aspect to the present invention.

FIGS. 21( a)-21(c) are various perspective views of a compression toolaccording to yet another aspect of the present invention.

FIGS. 22( a)-22(b) are side elevational views of the arms of analternate embodiment compression tool.

FIG. 23 is a side elevational view of a drill guide according to anotheraspect of the present invention.

FIG. 24 is a top plan view of the drill guide of FIG. 23.

FIG. 25 is a front elevational view of the drill guide of FIG. 23.

FIG. 26 is an enlarged front elevational view of a distal portion of theguide members forming a portion of the drill guide of FIG. 23.

FIG. 27 is a medial side elevational view of the distal portion of oneof the guide members of FIG. 26 looking in the direction of arrows 27-27of FIG. 26.

FIG. 28 is a cross-sectional view taken through line 28-28 of FIG. 27.

FIG. 29 is a top perspective view of the drill guide of FIG. 23positioned on a plate located on a spinal column segment.

FIG. 30 is an enlarged bottom perspective view of the plate and drillguide of FIG. 29.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the illustrated devices, and any further applications of theprinciples of the invention as illustrated herein, are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

A plating system 30 having application in an anterior approach to thecervical spine is depicted in FIGS. 1-3. The portion of the spine isshown schematically in FIG. 1 to include a first vertebra V1, a secondvertebra V2, and intermediate vertebrae V3 and V4. Preferably, firstvertebra V1 is the inferior or bottom vertebra in the portion of thespinal column and the second vertebra V2 is the superior or top vertebraof the portion of the spinal column. However, it is also contemplatedherein that first vertebra V1 is the superior vertebra and that secondvertebrae V2 is the inferior vertebra. It should also be understoodthat, as described below, the present invention has application withspinal column portions that include vertebrae ranging in number from twoto six vertebrae. One or more implants I may be placed into one or moreof the disc spaces between adjacent vertebrae as needed. Implant I maybe a bone graft, fusion device, or any other type of interbody devicethat is insertable into a disc space and promotes fusion betweenadjacent vertebrae.

In accordance with the present invention, the plating system 30 includesan elongated plate 31 having a number of openings therethrough and anumber of bone engaging fasteners, shown in the form of bone screws 50,that are insertable through the openings. In a preferred form, each boneengaging fastener is in the form of a bone screw. Plate 31 has alongitudinal axis L extending along the length of the plate at itscenterline. Bone engaging fasteners or bone screws 50 are held in plate31 by way of a retainer assembly 33 positioned along axis L. Theopenings of elongated plate 31 include a pair of holes 34 at first node36 adjacent a first end of plate 31. First node 36 is positioned overfirst vertebra V1. Plate 31 also includes a pair of slots 35 at a secondnode 37 adjacent a second end of plate 31. Second node 37 is positionedover second vertebra V2. In some forms of plate 31, several intermediatenodes 38 are provided along the length of the plate 31 between firstnode 36 and second node 37. Each intermediate node 38 includes a pair ofintermediate slots 32 positioned over a corresponding one of theintermediate vertebrae V3 and V4. Plating system 30 can be fabricatedfrom any type of biocompatible material.

It is preferred that holes 34 are paired with one of the holes of thepair on one side of the longitudinal axis L and the other hole of thepair on the opposite side of axis L. Slots 32 and 35 are similarlyarranged in pairs. It is also preferred that paired holes 34 areidentical in shape and size, and are located symmetrically about theaxis L. Paired slots 35 are also identical in shape and size, and arelocated symmetrically about the axis L. The paired slots 32 atintermediate nodes 38 are also identical in shape and size, and arelocated symmetrically about the axis L. Plate 31 includes recessesbetween each of nodes 36, 37, 38 to reduce the outer contouring size ofthe plate. In addition, the recesses between each of the nodes providesan area of reduced material, allowing additional bending of the plate bythe surgeon as may be required by the spinal anatomy. Plate 31 has alength selected by the surgeon with nodes 36, 37, and, if needed, nodes38 to register with the patient vertebrae.

Plate 31 preferably includes a rounded upper surface 41 that is incontact with the soft tissue surrounding the spine when the plate isengaged to the spine. Rounded surface 41 reduces the amount of traumathat would be experienced by the surrounding soft tissue. The bottomsurface 42 of plate 31 is preferably configured to contact the vertebralbodies of the spine at each of the instrumented levels. In oneembodiment, at least a portion of bottom surface 42 can be texturedalong the length of the plate to enhance its grip on a vertebral body.

Holes 34 include a recess 45 adjacent the top surface of plate 31 thatallow the head of the bone engaging fastener, such as bone screw 50, tobe countersunk in plate 31. Similarly, intermediate slots 32 include arecess 46 around each slot 32 adjacent top surface of the plate, andslots 35 include a recess 47 around each slot 35 adjacent the topsurface of the plate. Preferably, slots 35 include a ramp 60 that, asdescribed further below, allows a dynamic compression load to be appliedto the spinal column portion upon insertion of screw 50 at second end 43of slot 35. Recesses 46, 47 also allow the head of screw 50 to becountersunk in plate 31 when inserted through a corresponding one of theslots 32, 35. A groove 39 extends along axis L of plate 31 andintersects with each of recesses 45, 46, 47 along the length of groove39. The end of plate 31 at second node 37 includes a notch 40, which ispreferably rounded with a radius R4 centered on axis L (FIG. 12.)

Retainer assembly 33 includes a washer 90 having a length thatsubstantially corresponds to the length of plate 31. Washer 90 defines aplurality of apertures 91. Each aperture 91 is provided at a bodyportion 93, 94, 95 that corresponds to vertebral nodes 36, 37, 38,respectively. A connecting portion 98 extends between and connects bodyportions 93, 94, 95. Each of the apertures 91 has a countersink 92extending therearound adjacent to the top surface of washer 90. Asdescribed more fully below, countersink 92 is tapered from a first widthat the first end of aperture 91 to a second width at the second end ofaperture 91, the first width being greater than the second width.Locking fasteners, shown in the form of screws 85, are positionable,each through a corresponding one of the apertures 91, to engage afastener bore 70 (see FIGS. 4( a)-4(f)) in plate 31 and couple washer 90to plate 31.

Consequently, retainer assembly 33 retains screws 50 placed into thevertebral bodies at each of the instrumented levels. Washer 90 istranslatable from an unlocked position (FIG. 1) for bone screw insertionto a locked position (FIG. 2) after screw insertion to contact the headof the bone screws in holes 34 and overlap the heads of bone screws inslots 32, 35. Preferably, washer 90 does not contact the heads of bonescrews in slots 32, 35, thus allowing translation of the bone screws inthe slots. Back-out of the bone screws in slots 32, 35 is prevented whenthe bone screw backs out from its seated position a sufficient amount tocontact washer 90. Preferably, washer 90 resides almost entirely withingroove 39 of plate 31 to minimize the overall height of the construct.

As shown in FIG. 1, retainer assembly 33 is in an unlocked conditionwith screws 85 at the second end of apertures 90. In the unlockedcondition, body portions 93, 94, 95 of washer 90 do not overlap holes 34and a portion of slots 32, 35, and enable insertion of the bone screws50 therein. Narrowed portions 98 of washer 90 allow bone screws 50 to beplaced through holes 34 and slots 35 to secure plate 31 to the vertebraeV1 and V2. If desired, the surgeon can also place bone screws 50 inintermediate slots 32 to secure plate 31 to vertebrae V3 and V4 asdeemed necessary. Plate 31 and bone screws 50 preferably interface inholes 34 such that rigid fixation of plate 31 to the first vertebra V1is achieved. Slots 35 are positioned over second vertebra V2, andinclude a second end 43 and a first end 44. As shown in FIG. 1, screw 50is initially is inserted at second end 43 of slot 35, allowingsubsequent translation of screw 50 in slot 35 from second end 43 tofirst end 44. For the purposes of clarity, only a single screw 50 isshown in slot 35; however, it is contemplated that bone screws areinserted in both slots 35. Bone screws 50 inserted in intermediate slots32 also translate from the second end 48 to first end 49 (FIG. 15) ofslot 32.

Once screws 50 are placed through holes 34 and in slots 32 and 35,washer 90 of retainer assembly 33 may be translated to its lockedcondition shown in FIG. 2. In the locked condition, body portions 93,94, 95 of washer 90 retain the heads of the inserted screws 50 in holes34 and slots 32, 35 and prevent the screws from backing out of plate 31.In order to translate the retainer assembly 33 to its locked condition,locking screw 85 is threaded into a corresponding fastener bore 70 inplate 31. This downward threading of locking screw 85 causes the taperedcountersink 92 of washer 90 to ride along the head of locking screw 85until locking screw 85 contacts the first end of aperture 91. Thistranslates washer 90 along axis L to its locked condition, where thewasher 90 retains bone screws 50 in plate 31.

Bone screws 50 are allowed to translate within slots 35 and intermediateslots 32 from the second end of the slots to the first end of the slotswhile retainer assembly 33 retains bone screws 50 in plate 31 andprevents screw backout. As shown in FIG. 3, the screw positioned in slot35 has translated from second end 43 to first end 44. The translation ofscrew 50 is limited by contact of screw 50 with first end 44. The amountof translation may also be controlled by providing bone screws inintermediate slots 32. Thus, the amount of translation of the spinalcolumn segment can be limited by the length of slots 32, 35.

Referring now to FIGS. 4( a)-4(f) and FIGS. 5( a)-5(f), severalembodiments of elongated plate 31 and washer 90 are depicted. It isunderstood that the anterior plating system 30 according to the presentinvention can be readily adapted for fixation to several. vertebrae bymodifying the length of plate 31 and the number and arrangements ofholes 34, second slots 35, and intermediate slots 32. Paired slots 32,35 and paired holes 34 at each of the vertebrae provide, at a minimum,for at least two bone screws 50 to be engaged into each respectivevertebrae. The placement of two or more screws in each vertebral bodyimproves the stability of the construct. It is one object of the presentinvention not only to provide for multiple screw placements in eachvertebral body, but also to provide means for retaining the bone screwsin plate 31 to prevent back out or loosening of the screws. The presentinvention contemplates various specific embodiments for a plate 31 thatis provided in lengths that range from 19 millimeters (hereinafter “mm”)to 110 mm, and an overall width of about 17.8 mm. However, otherdimensions for the length and width of plate 31 are also contemplatedherein.

The plate 31 of FIGS. 1-3 is sized to span four vertebrae and includes afirst node 36, a second node 37, and two intermediate nodes 38. In FIGS.4( a) and 5(a), plate 31 a and washer 90 a are sized span two vertebrae.Plate 31 a has holes 34 a at first node 36 a and holes 34 a at secondnode 37 a. Plate 31 a is provided with washer 90 a that resides ingroove 39 a and is translatable to retain bone screws in holes 34 a. Inthis embodiment, plate 31 a provides rigid fixation at each vertebra. Amodification of plate 31 a is depicted FIGS. 4( b) and 5(b). The holesat the second vertebral node are replaced with slots 35 b at second node37 b. A washer 90 b resides in groove 39 b and is translatable to retainbone screws in holes 34 b and slots 35 b.

Plate 31 c and washer 90 c of FIGS. 4( c) and 5(c) similarly provide forinstrumentation at two vertebrae. Plate 30 c has a recess portionbetween nodes 36 c and 37 c. Washer 90 c resides in groove 39 c and istranslatable to retain lock screws in holes 34 c and slots 35 c. Itshould be noted that the plates of FIGS. 4( a)-4(c) span two vertebrae,and preferably do not include notch 40 on the second end of that plateas do the plates sized to span three or more vertebrae.

Plate 31 d and washer 90 d of FIGS. 4( d) and 5(d) are provided forinstrumentation at three vertebrae. Plate 31 d has first vertebral node36 d, second vertebral node 37 d, and intermediate node 38 d. Washer 90d resides in groove 39 d and is translatable to retain bone screws inholes 34 d and slots 32 d, 35 d. Plate 31 e and washer 90 e of FIGS. 4(e) and 5(e) are provided for instrumentation at five vertebrae. Plate 31e has first vertebral node 36 e, second vertebral node 37 e, and threeintermediate nodes 38 e. Washer 90 e resides in groove 39 e and istranslatable to retain bone screws in holes 34 e and slots 32 e, 35 e.Plate 31 f and washer 90 f of FIGS. 4( f) and 5(f) are provided forinstrumentation at six vertebrae. Plate 31 f has first vertebral node 36f, second vertebral node 37 f, and four intermediate nodes 38 f. Washer90 f resides in groove 39 f and is translatable to retain bone screws inholes 34 f and slots 32 f, 35 f.

Referring now to FIG. 6, the details of bone engaging fastener or screw50 are shown. Bone screw 50 is preferably configured for engagement inthe cervical spine, and includes threaded shank 51 that is configured toengage a cancellous bone of the vertebral body. The threaded shank maybe provided with self-tapping threads, although it is also contemplatedthat the threads can require prior drilling and tapping of the vertebralbody for insertion of screw 50. It is preferred that the threads onshank 51 define a constant outer diameter d2 along the length of theshank. It is also preferred that shank 51 has a root diameter that istapered along a portion of the length of the shank and increases fromthe tip of shank 51 to a diameter d1 at an intermediate or cylindricalportion 52.

Intermediate portion 52 extends between shank 51 and a head 54 of screw50. The threads on shank 51 extend into portion 52 by a thread run out53. According to standard machining practices, cylindrical portion 52includes a short segment that does not bear any threads. This segment ofcylindrical portion 52 interfaces or contacts with a plate thickness athole 34 or slot 32, 35 through which bone screw 50 extends. This shortsegment has an outer diameter d1. The head 54 of screw 50 includes atool recess 55 configured to receive a driving tool. In one specificembodiment, tool recess 55 is a hex recess, or in the alternative, anytype of drive recess as would occur to those skilled in the art. Head 54includes a truncated or flattened top surface 56 having a diameter d4. Aspherical surface 57 extends from cylindrical portion 52 to a shoulder59. Shoulder portion 59 has a diameter d5. An inclined surface 58extends between shoulder 59 and truncated top surface 56. Inclinedsurface 58 forms an angle A₁ with top surface 56.

It is contemplated that screw 50 may be provided with shank 51 having alength that varies from about 10 mm to about 24 mm. In one specificembodiment of screw 50, the threads have diameter d2 of about 4.5 mm. Inanother specific embodiment, the diameter d2 is about 4.0 mm. In bothspecific embodiments, cylindrical portion 52 has a diameter d1 of about4.05 mm. Cylindrical portion 52 has an unthreaded segment with a heighth1 that is determined by standard machining practices for thread run-outbetween a shank and screw head. Height h1 and diameter d1 of cylindricalportion 52 are sized to achieve a snug fit between screw 50 and plate 31in hole 34 or slot 32, 35 through which screw 50 is placed. Head 54 isprovided with height h2, outer diameter d5 at shoulder 59, diameter d4at top surface 56, and inclined surface 54 angle A₁ such that the head54 is nested within its corresponding slot 32, 35 or hole 34 andrecessed below the top surface of the plate. Although reference has beenmade to specific dimensions in this specific embodiment, it should beunderstood that the present invention also contemplates other dimensionsand configurations for screw 50. It should also be understood that bonescrews used to secure plate 31 can each have a different length anddiameters associated therewith, and need not correspond exactly to theother bone engaging fasteners used in the construct.

The details of locking screw 85 are provided in FIG. 7. Locking screw 85includes a shank 86 having machine threads thereon. In one specificembodiment, locking screw 85 terminates in a sharp point 88 that permitspenetration into the vertebral body when locking screw 85 is secured inthreaded fastener bore 70. Head 87 includes a lower conical surface 89configured to mate with aperture 91 of washer 90. Head 87 furtherincludes a tool recess 87 a for receiving a driving tool therein.

Further details and embodiments of washer 90 of retainer assembly 33 areprovided in FIGS. 8( a)-8(k). Washer 90 includes second body portion 95,first body portion 93, and if necessary, one or more intermediate bodyportions 94. A connecting portion 98 extends between and connects eachof the body portions 93, 94, 95. Washer 90 has a top surface 100 a and abottom surface 100 b. Each body portion 94, 95 defines an aperture 91extending between top surface 100 a and bottom surface 100 b. Aperture91 has a tapered countersink portion 92 therearound adjacent top surface100 b. Aperture 91 allows passage of shank 86 of locking screw 85therethrough, and countersink 92 is preferably configured to mate withconical surface 89 and seat locking screw 85 at various positions alongthe length of aperture 91. Preferably, countersink portion 92 is slopedtoward bottom surface 100 b from second end 97 to first end 96. Themating conical features between locking screw 85 and aperture 91 providea self-translating capability for washer 90 relative to plate 31 aslocking screw 85 is tightened into fastener bore 70 of plate 31.

Body portions 93, 94, 95 have a width W1 that is greater than a width W2of connecting portion 98. The width W1 and length of body portions 93,94, 95 are configured so that the body portions overlap with recess 45of holes 34 and recesses 46, 47 of slots 32, 35. The body portions 93,94, 95 retain the heads of bone screws extending through the holes andslots of plate 31 when washer 90 resides in groove 39 and is in thelocked condition of FIG. 2. The width W2 and the length of theconnecting portions 98 are configured to allow insertion of screws inholes 34 and slots 32, 35 when washer 90 is in the unlocked condition ofFIG. 1.

In FIGS. 8( a) and 8(b) there is shown second body portion 95 of washer90. Aperture 91 has countersink portion 92 that is tapered along thelength of aperture 91. Aperture 91 has a width W3 at bottom surface 100b of washer 90. Countersink portion 92 has a width that varies along thelength of aperture 91 and is greater than width W3. Countersink portion92 has a radius R1 at second end 97 and a radius R2 at first end 96 attop surface 100 a. It is preferred that R1 is less than R2 and the widthof countersink portion 92 increases from second end 97 towards first end96. Aperture 91 has a chord length S1 extending between the center ofradius R1 and the center of radius R2. Body portion 95 further includesa transition portion 99 that extends between connecting portion 98 andbody portion 95.

Intermediate body portion 94 of FIGS. 8( c) and 8(d) is similar in manyrespects to second body portion 95 of FIGS. 8( a) and 8(b), and alsoincludes an aperture 91 having a tapered countersink portion 92.However, intermediate body portion 94 has a connecting portion 98extending in both directions therefrom. A second transition portion 98 aextends between second connecting portion 98 and body portion 94. Bodyportion 94 has a chord length S1 between the center of radius R1 and thecenter of radius R2.

Tapered countersink 92 of aperture 91 provides a self-translatingcapability of the washer 90. This is because the washer 90 is translatedrelative to plate 31 as the locking screw 85 is threaded into threadedbore 70. The camming conical surface 89 of screw 85 advances downwardalong the tapered portion of the wall of countersink portion 92 ofaperture 91.

FIGS. 8( e) and 8(f) show first body portion 93. First body portion 93is also similar to second body portion 95. However, in one embodiment,first body portion 93 includes an aperture 91′ having a countersinkportion 92′ that is not tapered along its length to provide aself-translating capability for washer 90 like the countersink portions92 of body portions 94 and 95. Rather, after washer 90 is translatedrelative to plate 31 as described above, locking screw 85 will alreadybe positioned at first end 96′, and may thereafter be threaded into bore70 and seated within countersink portion 92′. Alternatively, the surgeonmay slide the washer by hand or with a tool to its translated position,and lock the washer in its translated position by seating locking screw85 into countersink 92′ at first end 96′. Countersink 92′ has a definitelocation at second end 96′ for seating locking screw 85, providing areference for the surgeon to confirm that washer 90 has been translatedto its locked position. It should be understood, however, that it isalso contemplated herein that body portion 93 could also be providedwith aperture 91 like body portions 94 and 95 as shown in FIGS. 1-3.

Referring now to FIG. 8( g), a cross-sectional view of washer 90 isprovided through aperture 91 of body portion 94, 95. Washer 90 has anouter surface 104 configured to overlap bone screws 50 in slots 32, 35without contacting inclined surface 58 of screws 50 when retainerassembly 33 is in its locked condition. Outer surface 104 extends frombottom surface 100 b to a shoulder 103. Shoulder 103 extends betweeninclined surface 104 and top surface 100 a. Inclined surface 104 formsan angle A₂ with respect to bottom surface 100 b. Washer 90 defines athickness t1 between top surface 100 a and bottom surface 100 b, and ashoulder height of t2 from bottom surface 100 b. Washer 90 has a widthW7 along bottom surface 100 b at aperture 91.

Referring now to FIG. 8( h), a cross-sectional view of washer 90 isprovided through aperture 91 or 91′ of body portion 93. Washer 90 hascontact surface 106 configured to contact inclined surface 58 of screws50 when retainer assembly 33 is in its locked condition. Contact surface106 extends from bottom surface 100 b to a shoulder 105. Shoulder 105extends between contact surface 106 and top surface 100 a. Contactsurface 106 forms an angle A₃ with respect to bottom surface 100 b thatis configured to mate with and provide surface contact with inclinedsurface 58 of bone screw 50. Washer 90 defines a thickness t3 betweentop surface 100 a and bottom surface 100 b, and a shoulder height of t4from bottom surface 100 b.

In one specific embodiment of the washer 90, the body portions have awidth W1 and connecting portion have width W2 that is based on thespacing between the centerlines of the paired slots and holes of theplates and the overall width of the plate. The width W3 of aperture 91in the specific embodiment is sized to accommodate the shank 86 oflocking screw 85 without head 87 passing therethrough. The length ofbody portions 94 and 95 varies based on the length and spacing betweenslots 32, 35 and holes 34 in plate 31. Preferably, the body portions 94,95 have a length sufficient to overlap substantially the entire lengthof slot 32, 35 when retainer assembly 33 is in its locked position. Thetapered countersink portion 92 of aperture 91 has radius R1 thattransitions to radius R2 along the chord length S1. Thickness t1 is lessthan thickness t3, and shoulder height t4 is less than shoulder heightt2. Body portion 93 has a width W8 along bottom surface 100 b that isgreater than width W7 of body portions 94, 95. Angle A₂ is preferablyless that angle A1. The dimensions of washer 90 are preferably arrangedso that body portions 94, 95 do not contact the screw heads nested inslots 32, 35 to facilitate translation of the screws in slots 32, 35.Body portion 93 contacts the screw heads nested in holes 34 to furtherenhance the fixed orientation between screws 50 and plate 31 in holes34. Although reference has been made to the dimensional attributes ofthis specific embodiment, it should be understood that the presentinvention also contemplates other orientations and dimensionalrelationships for washer 90.

The present invention also contemplates a retainer assembly in whichindividual washers are provided at each node for retaining screws inholes 34 and slots 32, 35 of plate 31. Referring now to FIGS. 8( i) and8(j), a slot washer 195 and a hole washer 193 are provided. Slot washer195 is similar to body portion 95 of washer 90 and hole washer 193 issimilar to body portion 93 of washer 90, both of which are describedabove. Elements that are alike bear the same reference number as thecorresponding element of body portions 95, 93. Slot washer 195 and holewasher 193 do not have a connecting portion 98 extending to anotherwasher. Slot washer 195 has a body portion 198 with a length S2 thatvaries and is sized to correspond to the length of the adjacent slot 32,35 when washers 195 are positioned on plate 31. Slot washer 195 does nothave a connecting portion 98 extending to another washer. Hole washer193 has a body portion 199 with a length S3 that varies and is sized tocorrespond to the length of the plate adjacent hole 34 when washer ispositioned on plate 31.

In FIG. 8( k) an alternate embodiment of washers 193 and 195 is providedand designated at 193′, 195′ respectively. Washers 193′, 195′ are thesame as washers 193, 195 described above, except for aperture 191.Aperture 191 does not have a tapered countersink, but rather has asemi-circular countersink portion 192 only at first end 196. Countersinkportion 192 provides a single position for locking screw 85 to lock thewasher 193′, 195′ to plate 31 after the washer 193′, 195′ has beentranslated relative to plate 31 by the surgeon. Washers 193′, 195′ havebody portion 198′,199′ with length S4 that varies as described abovewith respect to length S2 and S3.

Referring now to FIGS. 9-18, further details of plate 31 will bediscussed with reference to illustrations of first node 36, second node37, and intermediate node 38. In FIGS. 9-11, first node 36 of plate 31is depicted. It is preferred that holes 34 are identical and symmetricalabout axis L. Hole 34 includes recess 45 adjacent top surface 41. Holes34 include a cylindrical bore 77 having generally vertical sidewallsadjacent bottom surface 42. Cylindrical bore 77 extends between recess45 and bottom surface 42 of plate 31, and has a diameter D1. Cylindricalbore 77 has axis 72 b that is offset at angle A₅ from an axis 72 a thatextends normal to plate 31 as shown in FIG. 10. Recess 45 has a partialspherical portion 45 a defined about a central axis 72 b. Axis 72 b isoffset from axis 72 a by angle A₅. Offset angle A₅ directs bone screwsinserted into holes 34 toward the first end of plate 31. Furthermore, asshown in FIG. 11, axes 72 a converge below the bottom surface 42 ofplate 31 at angle A₄ with respect to an axis 72 c that extends along thecenterline of plate 31 perpendicular to axis L. Recess 45 intersectsgroove 39 at intersecting portion 45 c. Spherical portion 45 a isconfigured to mate with spherical surface 57 of bone screw 50, allowingat least a portion of head 54 to be recessed below top surface 41 ofplate 31.

To facilitate insertion of drill guides, drills and the bone screws 50,recess 45 also includes a flared portion 45 b that extends in a superiordirection from axis 72 b. In one embodiment, recess 45 includes a wallthat parallels bore 77 and extends between between spherical portion 45a and flared portion 45 b to further facilitate insertion andmaintenance of a drill guide in recess 45.

In one specific embodiment, spherical portion 45 a has a diameter thatmates with. the diameter of spherical surface 57 of screw 50, and isslightly larger than diameter d5 of head 54 of bone screw 50. Thecylindrical bore 77 of hole 34 has a diameter D1 of 4.1 mm, which isslightly larger than the diameter d1 of intermediate portion 52 of screw50. This portion of the screw contacts bore 77 and assumes a fixedorientation with respect to plate 31. In this specific embodiment,offset angle A₅ is about 12.6 degrees and convergence angle A₄ is about6 degrees relative to axis 72 c. Although reference has been made to thedimensional attributes of this specific embodiment, it should beunderstood that the present invention also contemplates otherdimensions.

Referring now to FIGS. 12-14, second vertebral node 37 is depicted.Vertebral node 37 includes slots 35 that are preferably identical andsymmetrical about axis L. Slot 35 includes slotted bore 78 adjacentbottom surface 42 of plate 31 having generally vertical sidewallsextending between second end 43 and first end 44. Slotted bore 78extends between bottom surface 42 and recess 47 adjacent top surface 42.Bore 78 has a width W5 and a chord length S4, and has a central axis 75b extending through plate 31. Recess 47 has a spherical portion 47 aabout central axis 75 b that extends around slot 35. As shown in FIG.13, central axis 75 b is offset from axis 75 a that extends normal toplate 31 by angle A₅. Offset angle A₅ directs bone screws inserted intoslot 35 towards the second end of plate 31. It should be noted that slot35 allows insertion of a bone screw at angles less than A₅ in slot 35,and bone screw 50 may be positioned within slot 35 at any locationbetween ends 43 and 44. However, retaining assembly 33 provides forinsertion of bone screws 50 at second 43 as would be clinicallydesirable for settling. Furthermore, as shown in FIG. 14, axes 75 bconverge below the bottom surface 42 of plate 31 at angle A₄ withrespect to axis 72 c.

Spherical portion 47 a is configured to mate with spherical surface 57of bone screw 50, allowing at least a portion of head 54 to be recessedbelow top surface 41 of plate 31. To facilitate insertion of drillguides, drills and the bone screws 50, recess 47 also includes a flaredportion 47 b that extends around spherical portion 47 a. In oneembodiment, it is contemplated that recess 47 include a wall thatparallels bore 78 extending between spherical portion 47 a and flaredportion 47 b to further facilitate maintenance and insertion of a drillguide in recess 47. Recess 47 intersects groove 39 at overlap portion 47c, as shown in FIG. 14. The second end of second node 37 includes notch40 having radius R4 centered about axis L. It is also contemplatedherein that plate 31 is provided without notch 40, as shown in FIGS. 4(a)-4(c).

In a preferred embodiment, slot 35 includes ramp 60 extending betweenbore 78 and flared portion 47 b at second end 43. Ramp 60 is notconfigured to allow spherical surface 57 of screw 50 to seat therein,but has an orientation that causes second end 43 of slot 35 and screw 50to separate as screw 50 is threaded into slot 35. Spherical surface 57of head 54 provides camming action along the ramp 60 until head 54 seatsin recess 47 at a position spaced a distance from second end 43. Thiscamming action applies a dynamic compression load to the spinal columnportion. The amount of compression applied to the spinal column portionis controlled by the length of ramp 60 from second 43 to the position inslot 35 where screw 50 seats in recess 47. It should be understood thatslot 35 may also be provided without ramp 60.

In one specific embodiment, spherical portion 47 a has a diameter sizedto mate with spherical surface 57 of screw 50, and is slightly largerthan diameter d5 of head 54 of bone screw 50. Slotted bore 78 has awidth W5 of about 4.1 mm, which is slightly larger than the diameter d1of intermediate portion 52 of screw 50. The cylindrical portion 52 ofbone screw 50 contacts plate 31 in bore 78 and prevents rotation ofscrew 50 transverse to axis 72 c. The chord length S4 varies dependingupon the length of the slot 35 needed for the particular application ofplate 31 and patient anatomy. In this specific embodiment, offset angleA₅ is about 12.6 degrees and convergence angle A₄ is about 6 degreesrelative to an axis 72 c. Although reference has been made to thedimensional attributes of this specific embodiment, it should beunderstood that the present invention also contemplates otherdimensions.

Referring now to FIGS. 15-17, various views of intermediate node 38 aredepicted. Vertebral node 38 includes slots 32 that are preferablyidentical and symmetrical about axis L. Slot 32 includes slotted bore 79adjacent bottom surface 42 of plate 31 having generally verticalsidewalls extending between a second end 48 and a first end 49. Slottedbore 79 extends between bottom surface 42 and recess 46 adjacent topsurface 42. Bore 79 has a width W5 and a chord length S5, and has acentral axis 76 a extending through plate 31. Recess 46 has a sphericalportion 46 a that extends around slot 35. As shown in FIG. 16, centralaxis 76 a generally extends normal to plate 31. However, as shown inFIG. 17, the axes 76 a converge below the bottom surface 42 of plate 31at angle A₄ with respect to axis 72 c. It should be noted that slot 32allows insertion of bone screws 50 at various angles with respect toaxis 76 a.

Spherical portion 46 a is configured to mate with spherical surface 57of bone screw 50, allowing at least a portion of head 54 to be recessedbelow top surface 41 of plate 31. To facilitate insertion of drillguides, drills and bone screws 50, recess 46 also includes a flaredportion 46 b that extends around spherical portion 46 a. In oneembodiment, a wall paralleling bore 79 extends between spherical portion46 a and flared portion 46 b to further facilitate insertion andmaintenance of a drill guide in recess 46. Screw 50 may be placed withinintermediate slot 32 between ends 48 and 49. However, it is preferredthat the screw is inserted initially at second end 48, thus allowingcompression loading of the spinal column segment. Recess 46 intersectsgroove 39 at overlap portion 46 c, as shown in FIG. 17.

In one specific embodiment, spherical portion 46 a has a diameter sizedto mate with spherical surface 57 of screw 50, and is slightly largerthan diameter d5 of head 54 of bone screw 50. The slotted bore 79 has awidth W5 of about 4.1 mm, which is slightly larger than the diameter d1of intermediate portion 52 of screw 50. Cylindrical portion 52 of bonescrew 50 interfaces with plate 31 in bore 79 such that angularadjustment of screw 50 transverse to axis 72 c is prevented. The chordlength S5 varies depending upon the length of slot 35 needed for theparticular application of plate 31 and patient anatomy. In this specificembodiment, convergence angle A₄ is about 6 degrees relative to an axis72 c. Although reference has been made to the dimensional attributes ofthis specific embodiment, it should be understood that the presentinvention also contemplates other dimensions.

Referring now to FIG. 18, a cross-sectional view of plate 31 is providedthrough line 18-18 of FIG. 15. Groove 39 has a width W6 at top surface41 of plate 31. Groove 39 has bottom surface 73 extending betweeninclined sidewalls 74. Sidewalls 74 extend between bottom surface 73 ofgroove 39 and top surface 41 of plate 31. It is contemplated that thegroove 39 has a depth sufficient to accommodate the washer 90 so as tominimize protrusion of washer 90 above top surface 41 of plate 31.

To accommodate the anterior application of the fixation plate assembly30, the plate is curved in two degrees of freedom. Specifically, thebottom surface 42 of the plate can be curved along a large radius R,centered in a vertebral plane containing central axis L, as shownschematically in FIG. 16, to accommodate the lordotic curvature of thecervical spine. In addition, bottom surface 42 forms a medial/lateralcurvature C, as shown in FIG. 18, to correspond to the curvature of thevertebral body. It is understood that plate 31 can also be bent asneeded to accommodate the particular spinal anatomy and vertebralpathology.

Referring now to FIG. 19 a, a partial sectional view of fixation plateassembly 30 at holes 34 is provided with screws 50 engaged to vertebraV1 and retainer assembly 33 in the locked position. A pair of screws 50are disposed within the respective holes 34 so that the threaded shanks51 project beyond the lower surface 42 of plate 31 into the vertebralbody V1. The intermediate portion 52 of screw 50 extends through thebore 77 of the hole 34. Spherical surface 57 of head 54 contacts recess45 of hole 34 when screw 50 is seated therein. The intermediate portion52 provides a snug fit for screw 50 in the bore 77 so that screw 50 isnot able to pivot with respect to plate 31.

Referring to FIG. 19 b, a partial sectional view of fixation plateassembly 30 at slots 32 or 35 is provided with screws 50 engaged tovertebra V1 and retainer assembly 33 in the locked position. A pair ofscrews 50 are disposed within respective slots 32, 35 so that threadedshanks 51 project beyond lower surface 42 of plate 31 into thecorresponding vertebral body V2, V3, or V4. Cylindrical portion 52 ofscrew 50 extends through bores 78, 79 of slots 35 and 32, respectively.Spherical surface 57 of head 54 contacts recesses 46, 47 of slots 32, 35when screw 50 is seated therein. Cylindrical portion 52 provides a snugfit for screw 50 in bores 78, 79 so that screw 50 is not able to pivotor translate with respect to axis 72 c of plate 31. Of course, screws 50inserted into slots 32 or 35 are able to translate along the length ofslots 32, 35 as described above. It should be understood that thepresent invention also contemplates various embodiments of plate 31 thatuse variable angle screws capable of assuming universal angularorientation with respect to plate 31 in slots 32, 35 and holes 34.

In order to ensure screws 50 are retained within plate 31, retainerassembly 33 is moved to its locked position where it contacts the heads54 of bone screws 50 in holes 34. Locking screw 85 is threaded intothreaded fastener bore 70 of plate 31 to translate washer 90 from itsunlocked position to its locked position, as described above, and todraw contact surface 106 into contact with inclined surface 58 of screw50 as shown in FIG. 19 a. Contact surface 106 preferably applies adownward force onto head 54 to firmly seat the screw heads within theplate recesses and further fix screw 50 in hole 34. In a preferredembodiment, this downward force is exacted by washer 90 as surface 106contacts inclined surface 58. As shown in FIG. 19 b, outer surface 104of washer 90 does not contact the heads of bone screws 50 in slots 32,25. Outer surface 104 overlaps the bone screws 50 to retain bone screwsin slots 32, 35. Outer surface 104 will contact the heads of the bonescrews if the bone screws backout from slots 32, 35. It is preferredthat bottom surface 100 b of washer 90 does not contact bottom surface73 of groove 39.

In a further aspect of the invention, the retainer assembly 33 may beloosely fixed on plate 31 so the surgeon need not fiddle with applyingretainer assembly 33 to plate 31 during surgical procedures. The lockingfasteners 85 are pre-inserted through apertures 91 of washer 90 andpartially threaded into fastener bores 70. Washer 90 is initiallypositioned such that the second end of each aperture 91 is positionedadjacent locking screw 85. After positioning screws 50 through the holesand slots of plate 31, locking fasteners 85 are advanced further intobores 70 and along tapered portions 92 of apertures 91 to translatewasher 90 to a locked condition and retain bone screws 50 in plate 31.

As previously mentioned, sharp point 88 of locking screw 85 ispreferably configured to penetrate the cortical bone. In one embodiment,sharp point 88 will penetrate the vertebra when plate 31 is initiallypositioned on the bone. In this instance, locking screw 85 helps locateand temporarily stabilize the plate on the vertebra as the bone screws50 are engaged to the vertebra. This temporary location feature providedby locking screw 85 can also be used to maintain the position of plate31 on the vertebra as a drill guide is used to drill and tap thevertebrae to receive bone screws 50.

According to another aspect of the invention, there are providedinstruments and techniques for securing plate 31 to vertebrae of aspinal column segment and for applying a compression load to a graft orimplant placed in the spinal column segment. Referring to FIGS. 20(a)-20(f), a guide 150 includes a handle 152, a template 154, and arm 153extending therebetween. Preferably, arm 153 extends outward from thespine and is bent so that handle 152 parallels the spine, positioninghandle 152 out of the way of the surgeon. Template 154 includes a secondend 155 that defines a notch 158. Template 154 also includes first end156 having a projection 156 a extending downward therefrom towardsvertebral body V2. Template 154 further defines a pair of slots 157between second end 159 and first end 156.

The surgeon selects a guide 150 with a template 154 sized to positionnotch 158 at the desired location on vertebra V2 and places guideinstrument 150 on vertebral body V2. Notch 158 is located on vertebra V2by placing projection 156 a in abutting contact with the endplate ofvertebra V2 in disc space D. Slots 157 provide a visual indication tothe surgeon of the range of positions available for screw insertion intothe vertebral body through slots 35 of plate 31. If desired, the surgeoncan obtain a desired position or location of notch 158 and the desiredavailable range of bone screw positions on vertebra V2 by selecting aguide having a different sized template 154.

Referring now to FIG. 20( b), after the notch is in the desired positionon vertebra V2, a compression pin 170 is placed into vertebra V2 guidedby notch 158. Pin 170 includes a lower end 171 having a threaded portion(not shown) for attaching pin 170 to vertebra V2. The attachment portionis preferably threaded to screw into vertebra V2, but may also be smoothwith a spiked tip for insertion into the vertebra. Pin 170 also includestool engagement portion 172 to facilitate installation of pin 170 to thevertebral body. It is also contemplated that the surgeon can place pin170 on the vertebral body spaced away from notch 158 if desired and thevertebral anatomy so allows.

After pin 170 is engaged to vertebra V2, guide 150 is removed and asleeve 180 is placed over pin 170 as shown in FIG. 20( c). Sleeve 180has a hollow body 181 extending between a first end 186 adjacentvertebra V1 and a second end 184. A second end 174 of pin 170 preferablyextends from second end 184 of sleeve 180, allowing access to pin 170.Sleeve 180 includes enlarged portion 184 to facilitate placement andremoval of sleeve 180. It is contemplated that sleeve 180 has hollowinterior and an internal configuration that provides secure attachmentto pin 170. Body 181 includes cylindrical outer surface 182 with anouter diameter d6.

With sleeve 180 in its proper position, plate 31 is positioned withnotch 40 in abutting contact with outer surface 182 of sleeve 180, asshown in FIG. 20( d). The diameter d6 of sleeve 180 slightly less thanthe twice the radius of notch 40 so that notch 40 is nested aroundsleeve 180. Plate 31 is then secured to vertebra V1 by inserting screws50 through holes 34.

With plate 31 secured to the vertebra V1, sleeve 180 is removed from pin170, as shown in FIG. 20( e), forming a gap 177 between pin 170 andnotch 40. In a preferred embodiment, it is contemplated that gap 177 isabout 2 mm. However, other sizes for gap 177 are contemplated hereinbased on the desired compression to be applied.

Referring now to FIG. 20( f), a compression tool 290 is secured to pin170 and to slots 32 of plate 31. It is also contemplated that thecompression tool can be secured to plate 31 other than at slots 32 by,for example, engaging the sides of plate 31. Compression tool 290 has afirst arm 291 with a first foot 294 connected to pin 170. Second arm 292is connected to the second end of slots 32 via extensions 297 extendingfrom second foot 296. First arm 291 and second arm 292 are manipulatedby the surgeon to apply a compression load to the spinal column segment.The amount of applied load is limited by gap 177 between pin 170 andnotch 40. For example, in the specific embodiment where gap 177 is 2 mm,the spinal column portion is compressed 2 mm.

Bone screws 50 are inserted into slots 35 with compression tool 290maintaining the compression load. With ramp 60 at second 43 of slot 35,an additional amount of dynamic compression is achieved with screwinsertion in slots 35, as described above. With screws 50 seated at end43 of slots 35, compression tool 290 may be removed without release ofthe compression load. Additional bone screws may be inserted intointermediate slots 32. Washer 90 may then be translated as describedabove to retain bone screws 50 in plate 31. It should be note that it iscontemplated herein that compression tool 290 and pin 170 are preferablyonly used with plates providing instrumentation at three or morevertebra. However, utilization of a compression tool configured toengage a plate for providing instrumentation at two vertebrae is notprecluded.

Referring now to FIGS. 21( a)-21(c), further details of compression tool290 are provided. Tool 290 has first arm 291 having first foot 294extending therefrom. First foot 294 defines recess 293 for receiving thepin 170. Second arm 292 has second foot 296 extending therefrom. Secondfoot 296 includes extensions 297 extending downward therefrom configuredto engage intermediate slots 32 of plate 31. Extensions 297 preferablyinclude recesses 307 that are configured contact the second ends ofintermediate slots 32. It is also contemplated that extensions 297 havea curved bottom surface 308 that corresponds to the medial lateralcurvature of the vertebral bodies.

First arm 291 has a reduced thickness portion 299 extending through apassage 295 formed in second arm 292, and is pivotally coupled to secondarm 292 with pin 299. First arm 291 has curved handle portion 306 havinga projection 303 extending therefrom. Second arm 292 has a handle 305. Aratchet bar 301 is pivotally coupled to second arm 292 via coupling 302.Preferably, ratchet bar 301 is spring-biased towards projection 303.Serrations 304 formed on the bottom side of ratchet mechanism 301provide for selective engagement with projection 303 on first arm 291.

The first and second arms are compressed towards one another to applythe compressive load to the vertebral segment. Projection 303 engagesthe serrated bottom of ratchet bar 301 to prevent relaxation of the armsand allows the surgeon to maintain the compression load during insertionof bone screws 50 within slots 35. Ratchet bar 301 may be lifted againstits spring bias away from arm 291 to disengage ratchet bar 301 fromprojection 303. Arms 291, 292 may then be moved away from one another torelease compression tool 290 from pin 170 and plate 31.

While compression tool 290 has been illustrated and described in detail,the present invention also contemplates other tools capable of beingsecured between pin 170 and plate 31 to provide a compression load tothe spinal column segment. For example, referring now to FIGS. 22( a)and 22(b), it is contemplated that a compression tool may include one ormore angular modifications to first arm 391 and second arm 392 tofacilitate access to plate 31 and pin 170 at the surgical site. Firstarm 391 has a lower portion 391 a forming angle BI with first foot 396.First foot 396 has extensions 397 extending therefrom that are similarto extensions 297 of tool 290. First arm has an upper portion 391 c thatterminates with curved handle 406. Curved handle 406 has projection 403extending therefrom to engage a ratchet bar extending from second arm392. Arm 391 has a vertical extension 391 b extending between lowerportion 391 a and upper portion 391 c. Angle B2 is formed between lowerportion 391 a and vertical portion 391 b. Angle B1 is formed betweenvertical portion 391 b and upper portion 391 c. Vertical portion 391 bas a region of reduced thickness 399 for connection with second arm 392.

Second arm 392 has a lower portion 392 a forming angle B1 with secondfoot 394. Second foot 394 has a recess (not shown) for receiving pin 170and is similar to recess 293 of tool 290 described above. Second arm 392has an upper portion 392 c that terminates with handle 405. Upperportion 392 c has ratchet bar 401 with serrations 404. Ratchet bar 401is pivotally coupled to arm 392 and spring-biased towards projection403. Ratchet bar 401 is similar to ratchet bar 301, but is preferablycurved along its length to accommodate the angular offsets in arms 391,392 while maintaining engagement between ratchet bar 401 and projection403. Arm 392 has a vertical extension 392 b extending between lowerportion 392 a and upper portion 392 c. Angle B2 is formed between lowerportion 392 a and vertical portion 392 b. Angle B1 is formed betweenvertical portion 392 b and upper portion 392 c. Vertical portion 392 bas a slot 395 of receiving reduced thickness portion 399 of verticalportion 391 b, where first and second arms are pivotally coupled via apin (not shown.)

In one specific embodiment of compression tool 290 and 390, angle B1 isabout 120 degrees and angle B2 is about 150 degrees. However, otherangular offsets in first and second arms of compression tools 190, 290are also contemplated herein as would occur to those skilled in the art.

Referring now to FIGS. 23-30, there will now be described methods andinstrumentation for drilling holes into the vertebrae in order to securethe plate to the vertebrae with bone engaging fasteners extendingthrough the plate and into the drilled holes. While the methods andinstrumentation of FIGS. 23-30 have application with the anteriorcervical plates described herein, it is also contemplated that themethods and instrumentation have application with plates secured toother areas of the spine, and also with plates secured to otherlocations on the vertebrae, such as the lateral, posterior, andantero-lateral aspects of the vertebrae. Further, while the drill guideof the present invention is described with respect to a plate P orientedwith slot SL over upper vertebra V2 as shown in FIGS. 29 and 30, it isfurther contemplated the drill guide has application with a plate havingone or more slots over one of or both of vertebrae V1 and V2.

In FIGS. 23-25, there is a drill guide 500 having a proximal handle 502coupled to a distal guiding portion 504. Drill guide 500 has a distalend 503 that is positioned in slots SL of plate P with plate P alignedover a portion of a bony structure, such as vertebrae V1, V2 and V3 asshown in FIG. 29. Plate P is to be secured to the bone with boneengaging fasteners, such as discussed above with respect to bone screw50; however, any suitable bone engaging fastener is contemplated. Drillguide 500 enables the surgeon to attain the desired orientation andpositioning to drill, and if desired or necessary, tap holes throughslot SL into the bone into which bone engaging fasteners are to beinserted to engage the plate therewith.

Guiding portion 504 includes a first guide member 506 and a second guidemember 508 interconnected by a connecting member 510 at proximal ends507, 509. Each guide member 506, 508 has a distal portion 511, 513 (FIG.26) respectively. It should be understood that the present inventionfurther contemplates a guiding portion that includes only one guidemember. First guide member 506 includes a passage 520 extending alongcentral axis C2, and second guide member 508 includes a passage 522extending along central axis C3. Passages 520, 522 are configured suchthat a drill bit may be passed therethrough and guided to its properposition and orientation through plate P and engaged to vertebra V2shown in FIG. 29. Central axes C2 and C3 are oriented such that holesdrilled through guide portions 506, 508 converge in the vertebral bodybelow plate P at an angle E1. In one specific embodiment, angle E1 is 12degrees to orient each hole and fastener at a 6 degree angle withrespect to central axis C1; however, other convergence angles E1 arealso contemplated. It is further contemplated that guide members 506,508 could be oriented such that holes drilled through guide members 506,508 diverge below plate P.

Handle 502 extends proximally from connecting member 510 such that itscentral axis C1 is centered between guide members 506, 508. Handle 502includes a distal portion 512 extending from connecting member 510 thathas a central axis C4 forming angle E2 with axes C2, C3 of guide members506, 508. A central member 514 extends from distal portion 510 and hascentral axis C1 forming angle E3 with axis C4. A proximal portion 516having a gripping portion 518 extends from central member 514 and has acentral axis C5 forming angle E4 with axis C1. Angles E2, E3, and E4offset handle 502 from the proximal end openings of guide members 506,508 to provide the surgeon clear access for inserting the drilltherethrough. In one specific embodiment of drill guide 500, angle E2 is102 degrees, angle E3 is 58 degrees, and angle E4 is 122 degrees. Inthis embodiment, angle E2 provides a 12 degree cephalad angle for thedrilled hole if the slot is positioned over the upper vertebra V2, or a12 degree caudal angle for the drilled hole if the slot is positionedover a lower vertebra V1. However, it should be understood that othervalues for angles E2, E3 and E4 are also contemplated. Furtherembodiments are also contemplated in which handle 502 is not offset fromthe proximal end openings guide members 506, 508.

Referring now to FIG. 26, further details regarding the distal portions511, 513 of guide members 506, 508 will now be described. Passage 520has an upper portion 520 a sized to allow passage of at least a portionof the drill therethrough. Passage 520 further includes a lower portion520 b sized to closely fit with the drill bit to help maintain itsproper alignment through guide member 506. It is contemplated that theheight H3 of lower portion 520 b is great enough to receive a length ofthe drill bit to ensure it is properly oriented with respect to vertebraV2 before the hole is drilled in vertebra V2. Passage 522 similarlyincludes an upper portion 522 a and lower portion 522 b. Rims 520 c, 522c are formed in each drill guide between the upper and lower portions ofpassages 520, 522, respectively, and can serve as or contact a depthstop on the drill to limit penetration depth of the drill bit into thevertebral body. The proximal ends of guide members 506, 508 couldsimilarly function to contact or act as a depth stop.

Guide member 506 further includes a main body portion 532 that extendsfrom proximal end 507 to an intermediate portion 528. Intermediateportion 528 extends about lower portion 520 b of passage 520 and has awidth in the direction of the slot width that is less than that of mainbody portion 532. Intermediate portion 528 is sized such that it can bepositioned in a recess extending around the plate slot SL withoutpassing through slot SL (FIG. 30.) A slot engaging portion 530 alsoextends about lower portion 520 b of passage 520 and further extendsfrom intermediate portion 528 to distal end 534 of guide member 506.Slot engaging portion 530 has a width in the direction of the slot widththat is less than that of intermediate portion 528. Slot engagingportion 538 is sized to reside in plate slot SL and in contact with theslot sidewalls with distal end 534 in close proximity to or in contactwith the bone underlying plate P.

Guide member 508 similarly includes a main body portion 538 that extendsfrom proximal end 509 to an intermediate portion 536. Intermediateportion 536 extends about lower portion 522 b of passage 522 and has awidth in the direction of the slot width that is less than that of mainbody portion 538. Intermediate portion 536 is sized such that it can bepositioned in a recess extending around the plate slot SL withoutpassing through slot SL (FIG. 30.) A slot engaging portion 538 alsoextends about lower portion 522 b of passage 522 and also extends fromintermediate portion 536 to the distal end 540 of guide member 508. Slotengaging portion 538 has a width in the direction of the slot width thatis less than that of intermediate portion 536. Slot engaging portion 538is sized to reside in plate slot SL in contact with the slot sidewallssuch that distal end 540 is in close proximity or in contact with thebone underlying plate P.

Guide member 506 includes a medial notch 524 formed therein extendingproximally from distal end 534. Guide member 508 similarly includes amedial notch 526 formed therein extending proximally from distal end540. Medial notches 524, 526 are oriented toward one another, and aresized to accommodate a fastener retaining member therebetween, such asthe washers for the retaining assemblies described above, so that guidemembers 506, 508 do not interfere with movement of the washer alongplate P. It is also contemplated that guide members 506, 508 areprovided without notches 524, 526.

Referring now to FIGS. 27-28, guide member 506 will be furtherdescribed, it being understood that guide member 508 includes identicalfeatures. Guide member 506 includes an offset portion 542 that extendsalong intermediate portion 528 and slot engaging portion 530. Offsetportion 542 extends along a side of guide member 508 such that it ispositionable against either the upper end or the lower end of slot SLwhen placed therein. In the illustrated embodiment of FIGS. 29-30,offset portion 542 is positioned in contact with upper end SL2 of slotSL.

Offset portion 542 has a contact surface 543 curved in a plane thatextends partially about passage 520 as shown in FIG. 28. As shown inFIG. 27, contact surface 543 of offset portion 542 is at least partiallycoplanar with the exterior surface of main body portion 532 such thatcontact surface 543 forms an extension of this exterior surface. Contactsurface 543 defines a curve having an offset center 544 and a radius R3measured from offset center 544. Offset center 544 is located along anaxis C5 that extends in the direction of the longitudinal axis SL1 ofslot SL (FIG. 30.) Axis C5 also extends though the center 546 of passage520, intersecting axis C2. Offset center 544 is offset from passagecenter 546 by a distance d3. In one specific embodiment, distance d3 is0.95 millimeters and R3 is 2.05 millimeters.

In an example of one specific application of the drill guide of thepresent invention, and with reference to FIGS. 29 and 30, plate P isplaced over vertebrae V1, V2 and V3 with holes HL aligned over vertebraV1 and slots SL aligned over vertebra V2. Holes are drilled throughholes HL and into vertebra V1 using known drill guiding instruments.Bone engaging fasteners are inserted through holes HL and into thedrilled holes to secure plate P to vertebra V1. Drill guide 500 is thenplaced in slots SL as shown in FIGS. 29 and 30 with contact surface 543against upper end SL2 of slot SL. Offset portion 542 spaces the adjacentedge of the hole drilled in vertebra V2 from the upper end SL2 of eachslot SL so that a bone engaging fastener inserted therein is spaced adistance d4 from upper end SL2. In one specific embodiment, this offsetdistance d4 is about 1.50 millimeters, however, offset distances of 1millimeter more are also contemplated. The holes are then drilledthrough guide members 506, 508 of drill guide 500 using manual or powerdrilling tools. Bone engaging fasteners are then inserted through slotsSL and into the offset holes drilled in vertebra V2, and are thus spaceda distance d4 from the upper end SL2 of slot SL. With the opposite endof plate P fixed to vertebra V1, and bone engaging fasteners offset inslots SL between its upper and lower ends, the plate P allowspost-operative settling of the spinal columns segment and alsoaccommodates extension of the spinal column segment, which is thought toimprove the environment for fusion incorporation of an interbody devicein disc space D2 and/or D1. Further, the surgeon can either distract orcompress the spinal column segment as desired since the bone engagingfasteners have space to move in either direction in slots SL.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications the come within the spirit of the inventionare desired to be protected.

1. A bone fixation system, comprising: a plate having a top and bottom surface and a central axis extending longitudinally between a first end and a second end, said plate having a plurality of openings between said top and bottom surfaces, wherein a pair of said openings are first and second slots positioned on opposing sides of said central axis, said first and second slots each having a width transverse to said central axis and a length extending between first and second ends of said slot in the direction of said central axis, said length being greater than said width; and a drill guide having first and second guide members extending from a handle, said first and second guide members each having a passage therethrough opening at a distal end of said corresponding guide member, wherein each of said guide members includes an offset portion adjacent said distal end positionable in a corresponding one of said first and second slots against said first end of said corresponding slot, wherein each of said offset portions is configured to space said first end of said corresponding slot from an adjacent edge of a hole formed through said guide member such that a fastener inserted into the hole through said slot is spaced a distance from said first end of said slot. 2.-26. (canceled) 